Disclosed in Japanese Patent Publication No. 31724-72, Japanese Utility Model Publication No. 14019-75 and Japanese Utility Model Laid-open Application No. 115504-74 are internal combustion engines having combustion chambers each of which is communicated via intake valves, with two intake passages, i.e., an intake passage for a heavy load and a general intake passage, whereby intake gas is supplied through the general intake passage while the engine load is light; otherwise, intake gas is supplied through both general and heavy load intake passages while the engine load is heavy. In addition, disclosed in Japanese Patent Publication No. 1725-73 is an internal combustion engine having a plurality of intake valves wherein the number of the operating intake valves is changed in accordance with changes in the operating conditions of the engine. In the engines, when the engine load is heavy, since the cross-sectional area of the intake passages can be changed in accordance with changes in the engine conditions, a large amount of combustible gas mixture can be introduced into combustion chambers. However, when the engine load is light, the combustible gas mixture cannot be burnt stably in the engines.
It is well known that, when a swirl motion is generated in a combustible gas mixture within a combustion chamber of an internal combustion engine so that a turbulence is generated in the combustible gas mixture, the combustible gas mixture can be burnt stably; as a result, the amount of harmful contaminants emitted in the exhaust gas can be reduced and the fuel consumption can also be reduced. However, in the known engines, there is a problem in that the maximum output of the engine is low. This is because if a sufficient turbulence is generated by creating a swirl motion in the combustible gas mixture while the engine load is light, a sufficient amount of combustion gas mixture cannot be introduced into combustion chambers while the engine load is heavy.
To overcome such a problem, in Japanese Patent Laid-open Application No. 148718-77, a diesel engine is disclosed wherein two intake passages are communicated with a combustion chamber via intake valves. Only one of the two intake passages has a throttle valve which is closed when the engine load is light, and the other intake passage is formed in a helical port for generating a swirl motion in the combustible gas when the engine load is light and for introducing a large amount of intake gas into combustion chambers when the engine load is high. However, since valve lifts of the intake valves in the engine are constant regardless of the engine load, satisfactory operating characteristics of the engine cannot be obtained irrespective of the operating conditions of the engine.
The principal object of the present invention is to provide an internal combustion engine which can overcome the above-mentioned problem. More specifically, the present invention provides an internal combustion engine which can obtain satisfactory operating characteristics irrespective of the operating conditions of the engine and which can generate a sufficient amount of swirl motion and turbulences in the combustible gas mixture so that the combustion gas mixture is burnt stably; as a result, a reduction of the harmful contaminants in the exhaust gas and a reduction of the fuel consumption can be achieved when the engine load is light, and which can prevent a reduction of the maximum output of the engine because a sufficient amount of the combustion gas mixture can be introduced into combustion chambers when the engine load is heavy.
In the present invention, the above-mentioned principal object is achieved by a dual intake valve type internal combustion engine wherein a main intake valve adapted to generate a swirl motion in the intake gas and an auxiliary intake valve of a variable valve lift type are communicated with a combustion chamber.
It is preferable that, in the present invention, a main intake valve is operated by a main cam having a cam profile for low speed use, in synchronization with a crankshaft of the engine, that an auxiliary valve is operated in synchronization with the crankshaft of the engine and that the valve lift of the auxiliary valve is varied in accordance with the changes in the operating conditions of the engine.
In the embodiments of the present invention which will be explained later with reference to the accompanying drawings, an auxiliary valve is operated by a swingable rocker arm, the fulcrum of the swinging motion of which is variable or operable by a variable valve lift mechanism including an oil tappet therein, so that the auxiliary valve is closed when the flow rate of intake gas is small. However, it should be noted that not only the variable valve lift mechanisms illustrated in the accompanying drawings, but also any other known variable valve lift mechanisms may be applied to the present invention. In addition, it should also be noted that various types of known valve mechanisms which can generate a swirl motion in the combustible gas mixture are applicable to a main intake valve of the present invention.
In the attached drawings, three embodiments of the main valves are shown, i.e. (i) in the first embodiment, the main intake valve is communicated with a main intake port which is shaped into a helical port so as to generate a swirl motion while the combustible gas mixture passes therethrough, (ii) in the second embodiment, a main intake valve has a shroud formed on the back thereof for generating a swirl motion while the combustible gas mixture passes along the shrouds and (iii) in the third embodiment, a projection surrounding a part of the main intake valve is formed on the wall of the combustion chamber for increasing the flow resistance between the projection and the main intake valve so that the flow of the combustible gas mixture through a portion not surrounded by the projection creates a swirl motion.
Some embodiments of the present invention will now be explained with reference to the accompanying drawings.